Thermodepolymerization of plastic using induction heating

ABSTRACT

Methods and apparatuses to depolymerize plastic to create fuel are provided. Plastic feedstock is heated to a molten state. The molten plastic is further heated by electromagnetic induction to a vapor state. The plastic vapor is collected and the temperature of the plastic vapor is lowered to produce liquid fuel. The molten plastic can be heated by electromagnetic induction to a vapor by placing the molten plastic in a plurality of trays and traversing the trays over a plurality of induction coils wherein each of the induction coils produce a magnetic field to heat the trays.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 61/420,913, which was filed on Dec. 8, 2010, and is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to thermodepolymerization of plastic using induction heating.

BACKGROUND

Thermodepolymerization of plastic generally is the process of vaporizing plastic to allow it to depolymerize into lighter carbons to create kerosene and other forms of fuel. Existing processes heat plastic in large tanks using external heating elements or internal heating elements. These processes are inefficient as it takes a relatively long time to heat the plastic. Furthermore, existing processes do not provide an even distribution of heat. Still further, residue can buildup on the outer surface of the internal heating elements. This residue can absorb energy intended to heat the plastic thereby requiring more energy to be supplied to existing processes. Since plastic can be a weak conductor of heat and the feedstock can be comprised of a mixture of materials having different characteristics when heated, it is difficult to determine the amount of energy needed to break the hydrocarbon chains within the plastic since other materials will be drawing energy. In addition to determining the energy needed, it is important to control the heat flow to heat the plastic so that it melts and does not burn.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example process to depolymerize plastic to create fuel.

FIGS. 2A and 2B illustrate an example system to depolymerize plastic to create fuel.

DETAILED DESCRIPTION

Various implementations of this disclosure provide apparatuses and methods to depolymerize plastic to create fuel.

FIG. 1 illustrates an example process 100 to depolymerize plastic to create fuel. The plastic feedstock used to create fuel may contain non-polymer impurities such as, glass, paper, and metal scraps. Therefore, at stage 105, the plastic feedstock is cleaned to reduce or remove impurities.

At stage 110, the plastic feedstock is heated to a molten state. In some implementations, an extruder can be used to raise the temperature of the plastic feedstock to place the plastic feedstock in a molten state and purify the plastic from any chemical substances. In some implementations, the temperature of the plastic feedstock is raised to 260° C.

There are other methods and apparatuses that can be used to preheat and purify plastic. This disclosure is not limited to any particular method to preheat and purify plastic.

At stage 115, the molten plastic is further heated by induction until thermodepolymerization occurs. In some implementations, the molten plastic can be heated by placing the molten plastic in heat transfer trays that are heated by electromagnetic induction systems.

At stage 120, the plastic vapor is collected and its temperature is lowered to produce liquid fuels. In some implementations, the plastic vapor is collected in a condenser which converts the plastic vapor into various forms of fuel.

In some implementations, the heating transfer trays can be cleaned at stage 125 and then the process can repeat at stage 105.

FIGS. 2A and 2B illustrate an example system 200 to depolymerize plastic to create fuel. The system can include an extruder 205, heat transfer trays 210, induction system 215, condenser 217, conveyor system, and cleaning brush 225.

The extruder 205 can be used to preheat the plastic and burn any impurities. After the plastic is purified and turned into its liquid form, it is deposited into trays 210.

Each tray 210 can be positioned on top of an induction system 215 (e.g., an induction coil) to heat the plastic in batches by electromagnetic induction. More specifically, an induction heating system 215 can turn a metal object such as tray 210 into a heating element by focusing its magnetic flux on the object.

In some implementations, each of the induction heating systems 215 passes alternating current through induction coils to create a magnetic field around the coils. The strength and penetration depth of the magnetic field is controlled by the amount of electricity/power passed by the induction system 215 to the coils and the frequency of the electricity respectively. Thus, an induction system 215 can aim and focus its energy on a specific area e.g., the tray 210.

In some implementations, the shape of the coils is configured to have the same geometry as the bottom of the tray 210 to concentrate the magnetic field on the tray 210. However, this disclosure is not limited to any particular shape of the induction coils.

As the tray 210 passes over top of the induction coils and through the magnetic field, the magnetic field creates eddy currents inside the material of the tray 210. A voltage drop can be associated with a given eddy current and consequently through resistance the electrical energy can be converted to thermal energy. The thermal energy can heat up the tray 210 thereby turning it into a heating element. Thereafter, the tray 210 conducts the heat onto the plastic inside the tray thereby causing the plastic to vaporize.

A condenser 217 can be used to collect and lower the temperature of the plastic vapor to produce liquid fuels.

In some implementations, each of the induction systems 215 can be individually controlled by a computer. For example, the plastic characteristics of the plastic in a tray 210 on top of an induction system 215 can be use as a feedback to the next induction system 215 that the tray 210 will traverse. Based on the plastic characteristics, the next induction system 215 can assign a heating pattern for the tray 210. Computer controlled induction systems 215 can help to ensures quality control and help minimize loss of material.

For example, the characteristics and temperature of the plastic in a tray can be determined by detecting changes in the phase of the plastic from a liquid to a vapor and detecting when it burns. As the plastic changes, the amount of heat the plastic absorbs from the tray can change. This change in heat absorption by the plastic can further change the amount of energy absorbed by the tray from the magnetic field. This change can be detected by meters, which can then notify the induction system to provide more or less power.

In some implementations, a group of induction systems 215 can be controlled by a computer.

To maximize the contact surface area between the molten feedstock and a heat transfer tray 210, in some implementation, each tray 210 has a relatively large surface area contact and small depth. In some implementations, the trays 210 include fins/rods 212 that extend from the bottom of the tray to the top of the tray. In some implementations, the fins/rods 212 can be evenly distributed in the tray for better heat distribution and faster diffusivity of heat in the plastic.

The tray 210 and fins/rods 212 can be made of ferrous material such as iron with high carbon content as these materials attract magnetic fields created by the induction coil and is most efficient in transferring the electrical energy of the magnetic field to thermal energy. In some implementations, the bottom of the trays 210 may be tilted toward the center to collect char. In some implementations, there may be a dip at the bottom center of the tray to collect residue.

In some implementations, the trays 210 are moved along by a conveyor system (e.g., such as conveyor system 220) since the trays 210 are not physically connected to any electrical terminals. The conveyor system can facilitate the movement of the heat transfer trays 210 through thermodepolymerization. The conveyor system also can allow for the feedstock to be continuously added to the trays 210 by the extruder 205 while the char and solid waste is continuously removed from the trays by a cleaning brush 225.

In some implementations, the conveyor system is placed in a housing 230 which is sealed from the environment to prevent product leak out or air leak in. The housing 230 also can be insulated on all exterior surfaces. The housing inner surfaces can be heated to the vapor temperature by the heat radiated from the plastic thereby eliminating any condensation of the plastic vapor in the interior of the system.

In some implementations, an inert gas with a higher density than the density of plastic vapor can be included inside the heating chamber to separate the top half of the chamber from the bottom half thereby raising the vapor product to the condenser. FIG. 2A depicts a line 235 to illustrate an example line of demarcation for the top half of the chamber and the bottom half of the chamber.

As the trays 210 rotate around the conveyor system, they can be cleaned by a cleaning brush 225 to remove char that may have collected in the tray. The trays 210 also may be cleaned by raising the temperature to turn residue inside the trays 210 into char dust thereby making it easier to remove residue with the cleaning brush 225.

The design depicted above for the tray and the enclosure is just an embodiment. The trays can take a cylindrical form or any form that ensures large contact surface area.

Implementations of the device of this disclosure, and components thereof, can be realized by instructions that upon execution cause one or more processing devices to carry out the processes and functions described above.

The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output thereby tying the process to a particular machine (e.g., a machine programmed to perform the processes described herein). The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.

The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the above description, numerous specific details are provided for a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that embodiments of the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations may not be shown or described in detail.

While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

Particular implementations of the subject matter described in this specification have been described. Other implementations are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results, unless expressly noted otherwise. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some implementations, multitasking and parallel processing may be advantageous. 

1. A method to depolymerize plastic to create fuel, comprising: heating plastic feedstock to a molten state; heating the molten plastic by electromagnetic induction to a vapor state; and collecting the plastic vapor and lowering the temperature of the plastic vapor to produce liquid fuel.
 2. The method of claim 1 wherein heating the molten plastic by electromagnetic induction to a vapor state comprises: placing the molten plastic in a plurality of trays; and traversing the trays over a plurality of induction coils wherein each of the induction coils produces a magnetic field to heat the trays.
 3. The method of claim 2 further comprising controlling an induction coil based on one or more characteristics of the plastic in a tray.
 4. The method of claim 3 wherein the characteristics of the plastic is the state of the plastic and/or the type of plastic.
 5. A system to depolymerize plastic to create fuel, comprising: an extruder to heat plastic feedstock to a molten state; a plurality of trays to hold the molten plastic; and an induction system to heat the trays by electromagnetic induction to heat the molten plastic to a vapor state.
 6. The system of claim 5 further comprising a condenser to collecting the plastic vapor and lower the temperature of the plastic vapor to produce liquid fuel.
 7. The system of claim 5 wherein the trays comprise a plurality of rods extending from the bottom of the tray.
 8. The system of claim 5 further including a processor to control the induction system based on one or more characteristics of the plastic in the trays.
 9. A system to depolymerize plastic to create fuel, comprising: means for heating plastic feedstock to a molten state; means for heating the molten plastic by electromagnetic induction to a vapor state; and means for collecting the plastic vapor and lower the temperature of the plastic vapor to produce liquid fuel. 